Decomposable monotithic ceramic materials having an at least bimodal pore distribution and active metal centers located in the pores

ABSTRACT

The present invention relates to decomposable monolithic ceramic materials having an at least bimodal pore structure, in particular having micropores and mesopores or mesopores and macropores or micropores, mesopores and marcopores, optinally having metal centres located in the pores. The invention further relates to processes for producing the materials of the invention and to the use of the materials of the invention and the materials produced by one of the processes of the invention, in particular in catalysis and catalyst research and in medical technology and for the time-delayed release of active compounds in the pharmaceutical industry.

The present invention relates to decomposable monolithic ceramicmaterials having an at least bimodal pore structure, in particularhaving micropores and mesopores or mesopores and macropores ormicropores, mesopores and marcopores, as well as to said materialshaving metal centers located in the pores. The invention further relatesto processes for producing the materials of the invention and to the useof the materials of the invention and the materials produced by one ofthe processes of the invention, in particular in catalysis and catalystresearch and in medical technology and for the time-delayed release ofactive compounds in the pharmaceutical industry.

In general, porous ceramic materials can be produced by a large numberof processes; in the following presentation of the prior art, adistinction will be made between three groups of materials which areproduced by correspondingly different processes: (i) materials havingmicropores and mesopores, (ii) materials having macropores andmesopores, and (iii) materials having micropores, mesopores andmacropores. It should be stated right at the beginning that the porousmaterials produced by processes coming under (i) are merely in the formof powder and not a stable monolith and the porous materials obtained bythe processes (ii) and (iii) are not decomposable.

Porous ceramic materials having micropores and mesopores, in particularthose which are produced using amphiphilic substances in sol-gelprocesses, are described by way of example in the following reviewarticle: D. M. Dabbs and I. A. Aksay, Ann. Rev. Phys. Chem. 51 (2000)601-622. Although these materials have well-defined micropores andmesopores, they are obtainable only as powders. It is explicitly statedin the publication that “a necessary prerequisite for the possiblecommercial use [of such mesostructures] is the formation of controlledshaped bodies and structures in the form of continuous thin films,fibres and monoliths”, with the size of these shapes being said to be“above the microscopic particle size which has hitherto beensynthesized”.

An optically isotropic and transparent monolith can be obtained, atleast temporarily, by use of a liquid crystal phase as template in asol-gel process (cf., for example, K. M. McGrath et al., Langmuir 16(2000, 398-406), but the monolith silicate structure disintegrates intoa powder on drying. Analogously, the use of surface-active agents(surfactants) of the prior art, for example, ionic surface-activeagents, also leads to structures which disintegrate on drying and/orcalcination (cf., for example, C. H. Ko et al., Microporous andMesoporous Materials 21 (1998) 235-243). Unsatisfactory dimensionalstability, i.e. a pulver morphology, is even more pronounced in the caseof the known MCM-41 materials which were developed for the first time in1992 in research laboratories of the Mobil company.

In general, microporous and mesoporous structures can be produced andvaried particularly advantageously when nonionic block copolymers areused in place of the conventional ionic surface-active agents in thesol-gel process. Particular mention may be made in this context of thework of G. D. Stucky and his group (cf., for example, D. Zhao et al.,Science 279 (1998) 548-552). In these processes, amphiphilic triblockcopolymers act as templates for pore formation and determine theporosity of the silicon framework. The framework is in this case builtup in a sol-gel process by hydrolysis of a silicate precursor material.The mesostructures formed here display well-defined Bragg reflections inthe X-ray powder diffraction pattern, in particular also in the smallangle region. This indicates a high degree of order on a mesoscopiclength scale which is, however, only achieved on calcination (cf., forexample, P. Yang et al., Nature 396 (1998) 152-155). The importantadvantage of these processes is that block copolymers, in contrast toconventional surface-active agents, allow virtually continuous variationof the pore parameters, and this can be done in situ during thesynthesis. It can be achieved, for example, by adjustment of the ratiosof amounts, the composition, the molecular weight or the moleculararchitecture of the block co-polymers in the mixture. However,disadvantages are that all processes of the prior art in which theseblock copolymers are employed do not enable macropores to be obtainedand, in particular, that this porous material, too, is pulverulent andnot in the form of a monolith material.

Another class of sol-gel processes is based on the use of water-solublepolymers as templates. In contrast to the abovementioned processes,materials having mesopores and macropores but no micropores are obtainedin this way. A significant advantage of these materials is that monolithshaped bodies and not just powders can now be obtained. In this context,particular mention may be made of the publications of Nakanishi andcolleagues. Thus, for example, WO 95/03256 describes the production ofporous monolithic materials having macropores together with mesopores.These materials are obtainable by hydrolysis of silicate precursormaterials with subsequent sol-gel condensation in the presence ofwater-soluble polymers, for example poly(ethylene oxides) (PEO).

The significant features of the synthesis of porous monolithic ceramicsby the method of Nakanishi are (i) the change of solvent between anacidic solvent and a basic solvent, which makes a significantcontribution to enabling pore size and pore size distribution of themesopores to be controlled in a targeted manner, and (ii) thecalcination of the green body obtained after drying at hightemperatures, i.e. at at least 600° C. This calcination step isessential to the solution of the object of the invention stated in WO95/03256, namely the provision of vitreous columns which are stable totheir environment and are fully hardened and are tailored, inparticular, for applications in high-pressure liquid chromatography(HPLC). Silicate columns produced by this process are manufactured andmarketed as Chromolith™ by Merck (Darmstadt, Germany) and by EM Science(Gibbstown, N.J., USA).

A disadvantage of the above-mentioned process described by Nakanishi is,in particular, the fact that the vitreous monolith obtained isdimensionally stable but is also inert toward physiologicalenvironmental conditions (see the definition given below), in particularis not soluble in water or aqueous solutions. This is disadvantageousfor, in particular, delayed and time-controlled release of activecompounds in pharmacy and for the design of biodegradable or resorbablebioceramics in medical technology. The processes of the prior art thuslead exclusively to porous ceramic structures which are not degradablein the human body or are not suitable for the release of activecompounds. Furthermore, the lack of micropores in the monoliths producedby the Nakanishi method has to be regarded as a deficiency, sincetrimodal porous monoliths are not obtainable by this synthetic route.

In addition to porous materials that may be used, among others, ascatalytically active materials, materials having catalytically activemetal centers are described quite generally in the prior art. Forexample, mention may be made of the publications of the Fina companywhich relates to inter alia, solid, particulate catalyst systems basedon metallocenes or metal salt solutions which are particularly usefulfor the polymerization and/or copolymerization of olefins (cf., forexample EP 0 573 403, WO 98/02236 or U.S. Pat. No. 5,846,896). Thesedocuments demonstrate the general importance of active metal centerswhich can be obtained, for example, by immobilization of metallocenes ona support material. In the scientific literature, mention may also bemade of the work of J.-M. Basset and colleagues (cf., for example, V.Vidal et al. Science 276 (1997) 99-102) in this context. However, theprior art gives no information as to how such active centers based onmetallic compounds generally or on metallocenes can be obtained incombination with the decomposable monolithic material of the invention.

In general, the prior art does not describe any ceramic materials whichare at the same time microporous, mesoporous and macroporous and, inparticular, does not describe any materials which are, in addition,monolithic and decomposable under physiological conditions. In addition,the prior art does not disclose any process which would be suitable forproducing such materials. Thus, EP 0 978 313 A1 does describe a materialhaving a trimodal porosity (micropores, mesopores and macropores), butthis is only obtainable as a composite comprising active carbon in asilicate framework, i.e. the trimodal porous structure is obtained in asubsequent step and not intrinsically and in situ during the productionprocess. Furthermore, this material is not a ceramic material (seedefinition given below) for the purposes of the present invention, sinceactive carbon as substantial constituent means that the material is nota ceramic material.

The prior art regarding the controlled and/or time-delayed release ofactive compounds is essentially characterized by conventionaltechniques, i.e. the pressing of tablets containing slowly dissolvingcomponents or the encapsulation of the active component in a shell whichdecomposes in the stomach, (cf., for example JP 632 430 36, in which theretention of active compounds by mixing silicates and cellulose isdescribed, and also U.S. Pat. No. 5,869,102, which is similarlyconcerned with the joint pressing of active compound, colloidalsilicates and microcrystalline cellulose). These are obviously processesin which the active compound is released in macroscopic amounts, i.e. inpulses, after decomposition of the shell and/or other constituents, therelease rate is essentially independent of the active compound used andlocal application and the release rate cannot be varied over aparticularly wide range or be controlled particularly precisely.

Accordingly, it is desirable and the objective of significant efforts inresearch and development to immobilize active compounds in microscopicor mesoscopic “cages” in a targeted and active compound-specific mannerand then to release them at a predetermined point in time in a specificlocation (e.g. gastrointestinal tract, forming tissue in the healing ofwounds, etc.) by dissolution of the cage structure. Such an approach isdescribed, for example, in F. Caruso et al., Chem. Mater. 11 (1999)3309-3314. This document is concerned with microvoids which are obtainedby coating colloidal spherical templates with nanosize particles andpolymers. Such hollow microstructures can, at least theoretically, beused for encapsulating active compounds, cosmetic substances or dyes andthen releasing them in a targeted manner. However, these materials aremerely clusters in solution and not a macroscopic monolithic material.

The general methodology of the targeted delivery of active protein andpeptide compounds (PP drugs), in particular by the peroral route, i.e.by oral intake and subsequent entry into the bloodstream via thegastrointestinal tract, is described, for example, in A. Sood and R.Panchagnula, Chem. Rev. 101 (2001) 3275-3303. For the purposes of thepresent invention, the approach described in this document as anin-principle possibility, namely carrying out the resorption of PP drugsfrom the gastrointestinal tract into the bloodstream with the aid ofnanosize particles, is of particular interest. It has been found thatparticles having a size of up to 5 μm can in actual fact be transportedintact and without any change in their properties through the intestinalwall into the bloodstream.

Mention may finally be made of a recently published process forproducing porous carbon-containing powders/crystallites using siliceoustemplates. In this process, carbohydrate-containing substances orcarbohydrates as precursor compounds are brought into contact with asiliceous template, e.g. MCM-48 and MCM-41. After drying andcalcination, the siliceous template can be removed, e.g. using HF and/orNaOH, to leave a carbon-containing porous powder or a porous powderconsisting entirely of carbon, having the pore structure of thesiliceous template. Particular mention may be made of the following twopublications: M. Kruk et al., J. Phys. Chem. B 104 (2000) 7960 and R.Ryoo, S. H. Joo and S. J. Jun, J. Phys. Chem B 103 (1999) 7743. However,according to the prior art, monolithic shaped bodies cannot be obtainedby this process.

It can therefore be stated in summary that although there are monolithicceramic materials having micropores and mesopores and correspondingmaterials having mesopores and macropores, there are no monolithicceramic materials which are dimensionally stable but neverthelessdecompose under physiological conditions, i.e. in particular in contactwith water. Such materials are of particular interest for the targetedand time-delayed release of active compounds and in medical technology.

Furthermore, the prior art discloses no monolithic ceramic materialswhich have pores at three levels, i.e. in principle the atomic level,the nanosize level and the micro level. Such hierarchical materials areof particular interest in catalyst research and nanotechnology.

Finally, there are no known ceramic materials which have at leastbimodal pore structure with active metal centers and are at the sametime monolithic and decomposable.

It is accordingly an object of the invention to provide a novel ceramicmonolithic material which has micropores and mesopores or mesopores andmacropores or micropores, mesopores and macropores and which should bedecomposable under physiological conditions, i.e. in particular for usein the pharmaceutical industry, medical technology, the cosmeticsindustry and the food industry. The materials used therefore have to be,in particular, biocompatible, nontoxic and biodegradable. A furtherimportant feature for the mass production of such materials is that thebase materials should be cheap and available in large quantities, i.e.the use of expensive block copolymers, for example should be avoided.Furthermore, it is an additional but optional object of the invention tomodify the novel porous ceramic material in such a way that at least oneactive metal center is present within the pores. Part of the object is,in particular, to provide a possible way of varying the acidity and/orthe redox behavior of the porous monolith of the invention.

The specific shape and/or size and/or porous structure of the monolithof the invention should be defined in the production process itself andnot only in a subsequent shaping step, as would be the case, forexample, in the compaction of a porous powder. The decomposable butdimensionally stable monolith should also be characterized by anamorphous structure, i.e. a structure having no grain boundaries betweencrystallites which could lead to crumbling of the material. Such anamorphous structure is indicated, for example, by the absence of Braggreflections in the X-ray diffraction pattern.

A particular object of the invention is also to provide monolithicceramic materials having mesopores, i.e. pores having a diameter in therange from 2 nm to 50 nm, in which the pore diameter can be set in atargeted manner and varied over a wide range. Pores of this diameter arenaturally of particular importance for applications of nanotechnology.

The object of the invention is achieved by providing a dimensionallystable and coherent monolithic ceramic material which can be regardedessentially as a hardened but not completely cured material, i.e. as anat least partially water-soluble, agglomeration of nanosize particles.In this material, the nanosize particles form a coherent framework,preferably a siliceous framework. On a complementary level, the coherentnanosize particles define a continuous, i.e. channel-like, network ofmicropores, mesopores (=nanopores) or micropores, i.e. material-freevoids.

Such a material can be obtained by various sol-gel processes which areessentially characterized in that at least one framework precursormaterial, at least one substance capable of hydrolysing the precursormaterial and at least one water-soluble polymer are combined. Thefurther addition of an amphiphile is optional, but is the basis of aparticularly important embodiment. The mixture obtained in this way isthen subjected to at least one sol-gel transition, a solvent replacementstep and a drying step. Depending on the embodiment, a calcination stepfollowing the drying step is mandatory, with the temperature of thecalcination step having to be chosen so that the material sets but doesnot harden to form an inert, vectoreous body, i.e. the material in eachcase remains at least partially decomposable under physiologicalconditions.

The incorporation of active metallic centers which relates to anotherimportant optional embodiment can be achieved either (i) in the sol-gelprocess for the production of the material of the invention by(co)hydrolysis of decomposable precursor materials in which metals arepresent or else by (ii) bringing the green body according to theinvention or the corresponding calcined materials into contact withreadily hydrolysable precursor compounds in which metals are present, inparticular metallocenes, in an after-treatment step. Both the acidity ofthe overall porous material and its redox behavior can then, as requiredby the object of the invention, be set at will via the type and amountof the active metal centers introduced by means of (i) and/or (ii).These two parameters can be set, in particular, independently of oneanother since the two methods (i) and (ii) of introducing active metalcenters are based on different principles and thus influence the acidityand redox behavior in different ways.

Definitions essential for the understanding and interpretation of thepresent invention are given below.

A property which is of particular importance for characterizing thematerial of the invention is its morphology, i.e. the material shouldnot be in the form of a powder but in the form of a coherent shaped bodywhich, for the purposes of the present invention, is referred to as amonolith. For the purposes of the present invention, monoliths ascoherent shaped bodies should have a dimension of at least 1 millimeterin all three directions in space. In principle, the monolith can haveany shape, i.e. for example plates, rods, spears (beads, pellets) or anyother conceivable geometric form. In particular, monoliths can also havecomplex shapes, for example, notches or grooves on the outsides with theaim of improving transport and/or flow properties around the monolith.In a practical embodiment, rods having a diameter of 5 mm and a lengthof from 5 to 10 mm are used.

For the purposes of the present invention, a ceramic material is anymaterial which has a higher proportion (in percent by weight) ofinorganic constituents than of organic constituents after the dry step.Organic constituents are, according to the invention, all constituentswhich contain exclusively compounds of carbon and optionally nitrogen,hydrogen, or oxygen. All other compounds are regarded as inorganicconstituents, in particular also those constituents which are referredto as “organometallic” or “organosilicone” compounds in chemistry textbooks.

Porous material quite generally are characterized, inter alia, by theirpore size, pore size distribution, type of pores simultaneously present,wall thickness of the frameworks surrounding the pores and their porevolume (porosity). On the basis of the pore size, a distinction is madebetween microporous materials, mesoporous materials and macroporousmaterials. The terms “microporous”, “mesoporous” and “macroporous” areused in the context of the present invention as they are defined in PureAppl. Chem., 45 (1976), p. 79, namely as pores whose diameter is above50 nm (macroporous) or in the range from 2 nm to 50 nm (mesoporous) orbelow 2 nm (microporous).

The pore size distribution can be narrow or broad, unimodal (onepredominant diameter), bimodal (two pore types of different size aresimultaneously present, with the mean pore sizes being further apartthan the sum of the two widths at half height) or trimodal (three typesof pores of different size are simultaneously present, with the meanpore sizes of adjacent types of pores being further apart than the sumof the corresponding two widths at half height). The pore sizedistribution (PSD) can be obtained, for example, by means of absorptionmeasurements. In the case of the present invention, the pore sizedistribution can be approximated well by a Gaussian bell curve. Themaximum of the bell curve gives the mean pore size. The full width athalf height, i.e. the width of the function at half the height betweenbaseline and maximum, is a measure of the broadness of the distribution.For most applications, a very narrow pore size distribution is sought.

Owing to inaccuracies in the methods of determining pore sizes, theassignment of pore types is undertaken within an error bar of two widthsat half height. Thus, for example, measurements on one of the materialsaccording to the present invention give a mean pore diameter which islocated at about 1 μm (1000 nm) at a width at half height of half amicron. These pores are thus unambiguously micropores. At the same time,the same material contains a further type of pore having a mean porediameter of 20 nm and a width at half height of 10 nm, i.e. these poresare unambiguously mesopores. Finally, the material contains a third typeof pore whose diameter is determined as 3 nm with a width at half heightof 1 nanometer and which, within the error range indicated above, can beassigned as micropores. In any case, this material is a material havinga trimodal pore structure, since all three mean pore diameters aresignificantly further apart than the sum of the relevant widths at halfheight.

Porous materials having a multimodal, i.e. at least bimodal, pore sizedistribution are also referred to as hierarchical. Different pore sizesare typically associated with different transport behavior. Thus, forexample, macropores are predestined for, in particular, “macroscopic”transport processes such as viscose or diffusive mass transport, whilein the case of mesopores, interfacial diffusion and capillary effectsdominate, and only activated transport takes place in micropores.Hierarchical pore structures thus result in hierarchical transportprocesses. It is thus possible, for example, for molecules to belocalized in one place in micropores for a prolonged period, but then berapidly transported away from this place by capillary or diffusivetransport in mesopores or macropores on activation or dissolution of themicropores. Such a mechanism is, for example, of interest for thepositionally and temporally localized release of active compounds inpharmaceutical applications. Similarly, a hierarchical pore structure isalso of interest for catalytic systems in which the rapid transport ofstarting materials and products to and away from the catalyticallyactive centers which are distributed in micropores having a high surfacearea occurs through mesoporous and macroporous transport channels.

For the purposes of the present invention, the term “decomposable”refers to dissolution and/or decomposition of the framework substance ofthe porous monolithic ceramic material under physiological conditions.Physiological conditions are all conditions which can occur in a livingorganism, in particular in the human body, especially in aqueoussolution, in saline aqueous solution, in acidic aqueous solution, inalkali aqueous solution and also particularly in saliva, in bodilyexcretion and transportation, especially in sweat, and in all secretionsfrom the body, in particular in mucus, and also in stomach juices, inthe intestinal tract, in blood or blood plasma, in connective or muscletissue and in bones or cartilage.

The novel monolithic ceramic material of the present invention ischaracterized in that it is at least bimodal and in that it is at leastpartially decomposable under physiological conditions, with the term“decomposable” being as defined above. In a preferred embodiment, the atleast bimodal material contains micropores and mesopores or mesoporesand macropores or micropores, mesopores and macropores, with the lattercase being particularly preferred.

In a further preferred embodiment, the material of the invention ischaracterized in that it displays no Bragg reflections in X-raymeasurements in the small angle region, i.e. in the angle range from 1°to 5° (when using a commercially available X-ray source, i.e. aconventional X-ray tube or a rotating anode which emits Cu—K_(α)radiation). Bragg reflections are the sharp peaks, i.e. peaks having ahalf width of a few widths at half height, known to those skilled in theart which indicate the presence of long- or intermediate-range order andcan be employed for indexing 2- or 3-dimensional ordered structures. Thecharacteristic Bragg reflections are found in the case of themicroporous and mesoporous materials obtainable according to the priorart (cf. for example, D. Zhao et al., Science 279 (1998), page 549) butnot in the case of the materials of the invention.

The material of the invention is, in a preferred embodiment, alsocharacterized in that it has not been heated to above 500° C. at anystage during its pre-treatment, production and/or after-treatment. Thisensures that the material is not cured completely to form a vitreousmaterial or a glass ceramic which would then not undergo at leastpartial decomposition under physiological conditions. The fact that thematerial of the invention must not be heated to above 500° C. during itspre-treatment, production and/or after-treatment does not rule outexposure of the material of the invention to a temperature higher than500° C. at some stage during its use, in particular in catalyticapplications.

In a further embodiment, the monolithic ceramic porous material of theinvention is characterized in that it has at least one further propertyselected from the following group, or has all of these properties:

-   -   the macropores are connected to form continuous transport        channels within which mass transport from one part of the        monolith to at least one further part can take place;    -   the size of the macropores, represented by the mean pore        diameter of plus/minus an error limit of two full widths at half        height, is from 50 nm to 1000 μm, preferably from 0.1 μm to 100        μm, particularly preferably from 0.5 μm to 30 μm;    -   the size of the mesopores, represented by the mean pore diameter        plus/minus an error limit of two widths at half height, is from        5 nm to 50 nm, preferably from 10 nm to 40 nm;    -   the size of the micropores, represented by the mean pore        diameter plus/minus an error limit of two widths at half height,        is preferably from 0.5 nm to 4 nm, particularly preferably from        1 nm to 3 nm;    -   the size distribution of the mesopores is such that the full        width at half height of the pore size distribution function is        ideally not more than 100% of the mean pore width, particularly        preferably not more than 50% of the mean pore width;    -   the material according to the invention after the drying step        has a higher proportion, measured in percent by weight, of        inorganic constituents than of organic constituents;    -   the material according to the invention after the drying step        comprises silicon and oxygen as main constituents, measured in        percent by weight.

The decomposable monolithic ceramic material of the invention having anat least bimodal pore structure can be produced by any conceivablemethod which leads to the above-mentioned material. In a preferredembodiment, it is produced by a process comprising at least thefollowing steps:

-   -   (I) bringing a precursor material, a water-soluble polymer and a        hydrolysis catalyst into contact with one another;    -   (II) inducing the sol-gel transition of the mixture from (I);    -   (III) removing and replacing the solvent in the gel from (II) or        removing or replacing the solvent;    -   (IV) drying the green body obtained from (III);    -   (V) calcining the dried green body at temperatures which do not        exceed 500° C. at any stage.

This preferred embodiment is a sol-gel process, i.e. polymerization of amolecular precursor material typically characterized by hydrolysis ofthe precursor material with subsequent condensation, i.e. formation ofan oxidic network. Depending on condensation conditions, in particulardepending on pH, linear polymers and long gel times or dense clusters ornanosize particles and short gel times, as well as, naturally, allintermediate states, can be obtained.

The materials obtainable according to the invention are (i) decomposableunder physiological conditions, (ii) biodegradable, (iii) nontoxic andgenerally compatible with living organisms and allow, at least in oneembodiment, (iv) setting of a trimodal pore structure which has nothitherto been known for these materials. Any combination of (i) and (iv)is conceivable.

The minimum starting materials to be used in the present embodiment are:(i) a precursor material, (ii) a substance suitable for hydrolysing theabove-mentioned precursor material, hereinafter referred to ashydrolysis catalyst, and (iii) a water-soluble polymer.

Hydrolysis and condensation of the precursor material results in theframework of the monolith to be produced in the sol-gel process. Asprecursor materials, it is in principle possible to use allpolymerizable substances having a low molecular weight, in particular:metal alkoxides, metal alkoxides having at least one nonhydrolysablegroup; polymerizable metal salts, in particular metal halogenides, andmetal hydroxides such as aluminium, iron, or bismuth hydroxides, andalso coordination compounds containing carboxyl or β-dicetone ligands.For the purposes of the present invention “metals” are not only themetallic conductors generally defined in textbooks, but also includesemimetals and semiconductors, i.e., in particular, B, Si, Ge, As, Se,Sb and Te. Alkoxides include, in particular, tetraethoxysilane (TEOS),tetramethoxysilane (TMOS), tetrapropoxysilane (TPOS) and polymerizedderivatives thereof; halides include halides which are decomposable inaqueous solution, in particular, chlorides such as SiCl₄, AlCl₄, TiCl₄,ZrCl₄, NbCl₅, TaCl₅, WCl₆ or SnCl₄. It is in principle also conceivableto use oligomeric precursor materials or organically modified silicates.A combination of two or more of the above substances is also possible.

The use of TEOS as precursor material is particularly preferred for thepurposes of the present invention. In case active material centers areto be incorporated into the inventive porous materials, preference isgiven to the use of precursor materials containing metals in combinationwith siliceous precursor materials, in particular TEOS. As precursormaterials containing metals, it is possible to use all metal-containingmaterials or metal-containing components or compounds mentioned in thepreceding paragraph, with the hydrolysable alkoxides of Zr, Ti, Nb, Ta,Al, Sn and Pb being particularly preferred. Production of the monolithicand decomposable ceramics of the invention using only precursormaterials containing metals is also conceivable.

The use of hydrolysable metal-containing components is a possible way ofobtaining the material according to the invention having at least oneactive metallic centre integrated into the pore structure. A furtherpossible route is indicated in the discussion of the after-treatment.For the purposes of the present invention, an “active metallic centre”is any metallic or metal-containing aggregation which comprises at leastone metal atom and is a constituent of the internal and/or externalsurface of the porous material of the invention, i.e. can have acatalytic action.

A significant advantage of this method of producing an at least bimodal,porous and monolithic material is the opportunity of setting the acidityof the catalytically active metal centers in a targeted way. The metalcan act as redox centre in a more or less strongly basic or acidicenvironment, for example determined by the ratio of TEOS to metalalkoxide and/or the use of admixed metal oxides or mixtures of metaloxides which are available in a wide variety and whose concentration canbe varied over a wide range. The catalytically active material of theinvention having metal centers of controlled acidity/basicity isaccordingly superior to, for example, conventional catalysts foroxidational reactions (for example vanadium oxide on a support), sincethe inherent acidity of the latter catalysts leads to reducedselectivity and a sufficiently large amount of basic additives thereforehas to be added subsequently.

As substance which leads to the hydrolysis of the precursor material,i.e. as hydrolysis catalyst, it is possible to use any substance whichat least partially promotes the hydrolysis of the precursor materials.These can be basic or acidic substances, with acidic substances beingpreferred for the purposes of the present invention since they generallylead to formation of condensed clusters (nanosize particles). Basicsubstances worthy of mention are a ammonium, amines and ammoniumhydroxide solutions. As acidic substances, mention may be of mineralacids such as nitric acid, sulphuric acid or hydrochloric acid andorganic acids such as acidic acid and also, in particular, hydrofluoricacid (HF) and fluoride-containing solutions in general.

The use of dilute mineral acids, in particular dilute nitric acid, anddilute organic acids, in particular dilute acidic acid, as hydrolysiscatalysts is particularly preferred for the purposes of the presentinvention.

Water-soluble polymers which meet the above-described requirements canbe selected from the group consisting of uncharged polymers, inparticular poly(ethylene oxides), poly(vinylpyrrolidones),poly(acrylamides), polyoles such as poly(ethylene glycols), polyoleswith formamide; ionic polymers, in particular polyacrylate acids,poly(alkalimetal styrenesulfonates), poly(allylamines), and alsocombinations of two or more of the above-mentioned substances.

The use of polyethylene glycol (PEG) as water-soluble polymer isparticularly preferred for the purposes of the present invention.

The medium in which the above-mentioned substances are combined in orderto carry out a sol-gel process is typically an aqueous medium, which inthe case of an acid being used as hydrolysis catalyst is naturallyacidic. A media containing alcohol's or other solvents and/or or saltsare likewise conceivable.

In addition to the above-mentioned substances which have to be combinedas a minimum in order to obtain the material according to the inventionin the sol-gel process of the invention, i.e. in addition to precursormaterial, hydrolysis catalyst and water-soluble polymer, it is possibleto add, if desired, any further auxiliaries, active compounds oradditives as long as these do not adversely affect the sol-gel processso that it can no longer be carried out as a whole. Such additional,optional materials can be selected from the group consisting of: salts,buffers, fibres, in particular cellulose; fillers; auxiliaries, activecompounds, additives, fragrances or flavours immobilized in theframework, in particular pharmaceutical active compounds, enzymes,proteins, peptides; swelling agents; thickeners; dyes, pigments;metal-containing components, in particular metal ions or colloidalmetals; polymerization initiators or inhibitors; and also combinationsof at least two of the above-mentioned substances.

The actual process for producing the material according to the inventioncomprises bringing the above-described components, which in thiscomposition are referred to as sol into contact with one another whilestirring in a step (I) and introducing the mixture into a mould, withthe mould naturally determining the exterior contours of the monolith.Specific ratios of amounts present in the sol and also absolute figuresfor weights are given in the examples. The range within which the ratiosmay vary in the preferred embodiments is indicated below. Thespecification of such amounts does not imply that other embodiments withdifferent ratios are excluded from the scope of the invention, butinstead serves merely for the purposes of illustration. These preferredratios lead to a material which is, in the sense of the presentinvention, dimensionally stable, i.e. give a monolith, and also has atleast some interlinked channels made up of connected macroscopic pores.The preferred molecular weight of PEG has been indicated above.

When TEOS and nitric acid are used together with PEG, a PEG content inthe range from 2 to 10% by weight based on the total weight ispreferred, with from 3 to 6% by weight being particularly preferred. Inthe case of a PEG content below 3%, the macropores are mostly isolated,while at a PEG content above 6%, the porous structure begins to breakdown and individual particles can be formed, i.e. the monolithicproperty is lost. The diameter of the macropores can be varied in therange from 1 to 80 μm by variation of the PEG content in the range from3 to 6% by weight, with a high PEG content corresponding to a smalldiameter of the macropores.

The relative proportion of TEOS (again when using TEOS, PEG and nitricacid) is indicated by the “r value”, which is the molar ratio of waterto Si (from the TEOS). For complete hydrolysis, for which four watermolecules are naturally necessary, the r value is 4. In a preferredembodiment, the r value (ratio of water content to TEOS) is from 10 to20, with an r value in the range from 12 to 18 being particularlypreferred. At large r values, i.e. at a low Si concentration,particulate aggregates are formed, while at low r values the macroporesare isolated, i.e. the transport channels are lost. The size of themacropores is likewise influenced by the r value, albeit not as greatlyas by variation of the PEG content, and is in the range from 80 μm(small r value) to 5 μm (large r value).

It should be stated at this point that the size and interconnectivity ofthe macropores is determined essentially by the ratios of PEG to thetotal mass and of TEOS to water, while the size of the mesopores isdetermined essentially by the characteristics of the solvent replacementdiscussed below.

After the components have been combined in the above-mentioned ratiosand the resulting sol has been introduced into the mould, the sol isconverted into a gel at temperatures in the range from 20° C. to 80° C.,particularly preferably about 40° C. When TEOS, PEG and nitric acid areused in the above-mentioned ratios, the gel time t_(gel) at 40° C. isfrom 4 to 6 hours (the optionally use of an amphiphile such as the CTAB,e.g. C₁₆ TAB, described below can result in a gel time in the range from4 hours to 12 hours).

After this sol-gel transition, the gel is aged for at least 48 hours.Ageing can be carried out in temperatures in the range from 20° C. to80° C., with a temperature of 40° C. being particularly preferred forthe purposes of the present invention. Ageing in the sense of theinvention is regarded as part of the sol-gel transition, i.e. part ofstep (II) and serves to strengthen the siliceous network (when TEOS isused) and thus to reduce or completely prevent crack formation in themonolith.

A next step in the process of the invention is step (III), namely theremoval of the solvent or the replacement of the solvent. Solvent can beremoved from the pores during ageing and drying. Solvent replacement iscarried out by dipping the gel into an aqueous solution having an acidicor basic character, depending on whether an acidic solvent (here, forexample, nitric acid) is to be replaced by a basic solvent or viceversa. Solvent replacement is essential to achieve a narrow poredistribution of the mesopores as a result of dissolution andredeposition of the matrix.

In the case of a gel which has been obtained from TEOS, PEG and nitricacid, replacement of the solvent by ammonium hydroxide solution is apreferred embodiment. The lower the concentration of ammonium hydroxide,the smaller the mesopores. The size of the mesopores can thus beadjusted by varying the ammonium hydroxide concentration, withconcentrations of ammonium hydroxide of from 0.01 mol/l to 2 mol/l beingpreferred. The mean pore diameter of the mesopores is from about 3 nm inthe case of a 0.02 molar solution to 16 nm in the case of a 2 molarsolution. The values for the pore diameter were in each case obtained bymeans of Hg porosimetry.

For this step, preference is given to a temperature in the range from40° C. to 95° C., particularly preferably from 70° C. to 90° C. Thelower the temperature, the smaller the mesopores. The solventreplacement is typically carried out for from 5 to 10 hours, with lowertemperatures requiring longer times. The volume of the replacementliquid should be about 10 times the volume of the monolith, but anyvalue for the volume ratio is possible in principle as long as themonolith is immersed completely in the solvent. On the subject of thesolvent replacement, the results of WO 95/03256 and of N. Ishizuka etal., J. of Chromatography 797 (1998) 133-137, are fully incorporated byreference into the present patent application.

Subsequent to the solvent replacement, the monoliths are washed (e.g.with 0.1 M nitric acid and subsequently with ethanol) and dried for 3days at about 60° C. This washing and drying step is regarded, for thepurposes of the present invention, as drying step (IV). The shaped bodyor monolith obtained in this way is referred as “green body” for thepurposes of the invention and can be employed for the use provided foraccording to the invention. In particular, the green body can besubjected to any after-treatments, e.g. impregnation or bringing intocontact with catalytically active substances, (pharmaceutical) activecompounds, vitamins, enzymes, peptides, plant extracts, phytotherapeuticagents, fragrances and flavours, auxiliaries, nutrients, cosmeticsubstances, dyes, etc. The green body according to the invention isdecomposable under physiological conditions, i.e. in particular, incontact with water. This means that all the above-mentioned substancescan be liberated again at a future point in time at a predeterminedlocation.

A preferred form of the after-treatment is functionalization of at leastpart of the internal surface formed by the micropores, mesopores ormacropores or the channels resulting there from. It can, for example, beachieved by reaction of the free hydroxyl groups of the frameworksubstance to convert them into different groups, for example estergroups. In a particularly preferred embodiment, for example, theinternal surface which is hydrophilic because of the hydroxy groups canbe made at least partially lipophilic.

In a further preferred embodiment of the after-treatment, a (preferablyreadily) hydrolysable precursor material containing at least onemetallic component is brought into contact with the material accordingto the invention (a green body prior to calcination or shaped body aftercalcination). These can be brought into contact with one another underall conditions mentioned below in connection with controlledatmospheres, i.e., in particular, under reduced pressure or under apressure above ambient pressure. They can be brought into contact bymeans of impregnation or deposition, with deposition being able to occurfrom the gas phase and/or the liquid phase. They can be brought intocontact either continuously, consecutively, (i.e. the micropores first,then the mesopores and/or macropores) or in any desired steps and/orintermediate states. After the materials have been brought into contactwith one another, hydrolysis of at least part of the hydrolysablematerial is induced. As the metal-containing precursor material, it ispossible to use all metal-containing substances which bind to the OHgroups present in the pores of the material according to the inventionand/or to other conceivable functional groups to form ester groups orform a stable bond in another way. For the purposes of the invention, abond is stable if it remains intact under the conditions of use. Themetal-containing precursor materials can be selected from the group ofmetal-containing precursor materials mentioned above in general terms inconnection with precursor materials. Organometallic compounds, metalsalts and colloidal metals are preferred and metallocenes areparticularly preferred.

The active metal centers formed in this way can, depending on theconcentration of the metal-containing precursor material brought intocontact with the interior walls of the pores, and depending on thefunctionality of the pores (density of the OH groups, reactivity of theOH groups, wetability of the pores, etc.), in principle occur in threedifferent functional modifications: (a) as individual active centers(single site catalyst), (b) as nanosize particles bound to the surfaceof a pore and (c) in the case of a sufficient density of centers, as afilm layer. Intermediate states, e.g. linear chains, branched paths orany combinations of the above-mentioned modifications are included aswell.

What has been said with regard to the functional modification alsoapplies analogously to active centers formed as described above by(co)hydrolysis of metal-containing precursor materials.

In a further preferred embodiment, the at least bimodal siliceousmonolith of the invention is brought into contact with at least onecarbon-containing precursor compound in the course of an after-treatmentstep. The carbon-containing compound can in principle be any substancewhich contains at least one carbon atom. Preference is given to alcoholsand carbohydrates. For the purposes of the present invention, “bringinginto contact” encompasses any introduction and/or application of thecarbon-containing precursor compound into/onto the porous siliceousmaterial. Preference is given to impregnation with a liquid solution,e.g. of sucrose or furfuryl alcohol. In the context of the presentinvention, the at least bimodal siliceous material according to theinvention then acts as template.

After impregnation, the now carbon-containing material according to theinvention can be treated further as described, for example, in the twopublications M. Kruk et al., J. Phys. Chem. B 104 (2000) 7960 and R.Ryoo, S. H. Joo and S. J. Jun, J. Phys. Chem. B 103 (1999) 7743. In thiscontext, both these publications are fully incorporated by referenceinto the present patent application. The further treatment isessentially a calcination at temperatures above 500° C., preferably atabout 1000° C., under nitrogen and subsequent carbonization underreduced pressure. The siliceous template can then be removed ifappropriate, for example, by treating the shaped body with HF and/orNaOH. This leaves an essentially carbon-containing porous monolithshaped body, or a porous monolith body consisting entirely of carbon,which has similar properties in terms of the pore structure as thesiliceous shaped body used as template. An advantage over the prior artis that use of the monolith according to the invention as template alsogives a carbon-containing monolith, i.e. not merely a porous powder.

In the calcination, i.e. in step (V), the green bodies are fired in anopen or controlled atmosphere. The temperature can be in the range fromthe drying temperature to 500° C. Temperatures in the range from thedrying temperature to 300° C. are particularly preferred. Thecalcination times depend on the desired degree of hardening and canrange from a few hours to a few days. The main purpose of thecalcination is, apart from the further hardening, to remove anyundesirable organic components. In principle, calcination can be carriedout before or after the after-treatment. Calcination prior to theafter-treatment influences, inter alia, the number of OH functions andthus may also influence the after-treatment. For example, a reducednumber of OH functions leads to a reduced number of metal-containingactive centers.

For the purposes of the present invention, controlled atmospheres are:inert gases, reducing atmospheres, for example hydrogen-containinggases, hydrothermal conditions, in particular stream, oxidisingatmospheres, reactive gases, atmospheres under superatmospheric orsubatmospheric pressure and also all possible combinations and/ormixtures of the above-mentioned atmospheres.

In a further, particularly preferred embodiment, not only a monolithicceramic decomposable material having a bimodal pore structure, i.e. withmacropores and mesopores or with micropores and mesopores, but amonolithic ceramic decomposable material having a trimodal porestructure, in particular with macropores, mesopores and micropores, isobtained. Here, all process steps are analogous to the above-describedsteps (I) to (IV), with the exception that a fourth component, namely anamphiphilic substance, is added in addition to the precursor material,the hydrolysis catalyst and the water-soluble polymer in step (I):

-   -   (I) bringing a precursor material, a water-soluble polymer, and        amphiphilic substance and a hydrolysis catalyst into contact        with one another;    -   (II) inducing the sol-gel transition of the mixture from (I);    -   (III) removing and replacing the solvent in the gel from (ii) or        removing or replacing the solvent:    -   (IV) drying the green body obtained from (III).

The amphiphilic substance has the task of providing a further templatefor pore formation (in addition to the water-soluble polymer which isresponsible for phase separation). Owing to the nature of this template,it forms pores having a smaller diameter than that of the mesoporeswhich are formed as a result of the addition of the water-solublepolymers. In particular, micropores, i.e. pores having a diameter of afew nano meters, are obtainable in this way. It needs to be particularlyemphasized that in the process of the invention, the micropores formedduring production of the material of the invention and are notintroduced only in a subsequent after-processing step. The approachprovided by the invention thus ensures that the distribution of thepores in the material is homogeneous. The amphiphilic substance isselected from the group consisting of block copolymers, in particularpoly(alkyl oxide), triblock copolymers; surface-active agents(surfactants), detergents and soaps, in particular non-ionic alkylpoly(ethylene oxides); lipids, phospholipids; and also combinations oftwo or more of the above-mentioned substances.

For the purposes of the present invention, the use of ionic surfactants,in particular hexadecyltrimethylammonium bromide, as amphiphilicsubstance is particularly preferred. For the purposes of the presentinvention, all amphiphilic substances having a trimethylammonium bromide(TAB) unit and a carbon chain of any length are referred to as “CTAB”.The number of carbon atoms in an individual case may be specified, forexample, C₁₆TAB in the present case. When an amphiphilic substance isused, calcination at temperatures above 500° C. may be necessary ifcomplete removal of the organic amphiphile is desired. If TEOS, PEG,nitric acid and CTAB are used as starting materials, a CTAB content offrom 0.01 to 5% by weight is preferred and a content of from 0.1 to 3%by weight is particularly preferred. Increasing the concentration ofCTAB within the range indicated influences the mesopores, namely bydecreasing their size, and also results in increased formation ofmicropores whose size extends from 1 nm to 5 nm and whose numberincreases with increasing CTAB concentrations.

As far as the incorporation of active metal centers and the steps of theafter-treatment are concerned, what has been said above with regard tothe corresponding bimodal material applies to the trimodal porousmaterial of the invention as well.

As regards the production of carbon-containing porous monolithic shapedbodies or porous monolithic shaped bodies consisting entirely of carbonas a consequence of an after-treatment of the trimodal porous siliceousmonolithic of the invention, what has been said above in the context ofthe bimodal monolith of the invention applies in full.

The monolithic ceramic material of the invention can be usedadvantageously in catalyst applications. This applies particularly tomaterials according to the invention which have active metal centers. Asdescribed above, these active metal centers can have been formed eitherin the sol-gel process or else by means of an after-treatment. Owing tothe opportunity of controlling acidity and/or redox behavior of theactive metal centers, the use of the catalysts of the invention for(partial) oxidation reactions is particularly preferred. It is naturallyalso conceivable for the material according to the invention to becatalytically active itself, i.e. without the presence of active metals,in particular as a result of its hierarchical pore structure. Allmaterials described in the present invention can be used directly ascatalysts, as support materials for catalysts and in catalyst research.

In a preferred embodiment, the acidity and the redox potential or theacidity or the redox potential of the metal-containing component(s) in acatalyst according to the invention containing a metal-containingcomponent can be varied together or independently of one another bymeans of at least one measure selected from the group consisting of:concentration of the metal-containing precursor material relative to theprecursor material containing no metal, type and composition of themetal-containing precursor material and density of the OH groups in thepores.

In related applications which exploit the pore structure, the materialof the invention can be used as molecular sieve, ion exchanger or asbiological separator having a sharp cut-off criteria in respect of themolecular weight, and also as osmotic membrane. Uses as waveguides, orsupport material for optical sensors; chemical or biological sensors arelikewise conceivable. In all cases, and in the applications given below,the presence of active metals centers is optional. In some cases, it maybe preferred to not use metal centers at all.

The above-described use of the material of the invention for thetemporally delayed and temporally controlled and regionally definedsupply of any substances, in particular dyes, cosmetic active compounds,auxiliaries or additives, nutrients or nutrient additives, animal feedsor animal feed additives, fragrances and flavours, is of particularimportance. Particular preference is given to the delayed or temporallycontrolled, but in any case regionally well-defined, supply ofpharmaceutically relevant active compounds in living organisms, inparticular in the human body, is particularly preferred.

In this context, the hierarchical pore structure is of particularinterest, since it makes it possible for the material of the inventionto be successively loaded and unloaded. Thus, for example, the activecompounds, auxiliaries or additives which are smallest can firstly beintroduced into the micropores, followed by larger active compounds,auxiliaries or additives into the mesopores and/or macropores. Whenmixtures are incorporated, in particular plant extracts orphytotherapeutic agents, it is even possible to obtain a “natural”separation of various components in this way. It is also conceivable forcell constituents or relatively larger peptide chains or the like to beincorporated in the macropores in addition to the active compounds,auxiliaries or additives which are typically molecular in nature and canbe incorporated in micropores or mesopores. In this context, attentionmay once again be drawn to the possibility of completely or partiallyfunctionalising the internal surface, in particular making itlipophilic. It is also conceivable for after-treatment and loading stepsto be combined, i.e., for example, firstly introducing a hydrophilicsubstance into the micropores and subsequently making the remainder ofthe internal surface lipophilic and then introducing a lipophilicsubstance.

As noted above in the discussion of the prior art, a significant newdevelopment is to encapsulate active compounds, in particular active PPcompounds (proteins and peptides) which are susceptible to enzymaticdecomposition and cannot be resorbed per se through membranes, innanosize particles and micro particles and thus, for example, transportthem through the intestinal wall into the bloodstream. The material ofthe invention is particularly useful for such applications, since it canbe regarded as an agglomeration of nanosize particles, with the cohesionof the nanosize particles being able to be adjusted by means of avariety of process parameters, for example, PEG or TEOS ? or degree ofhardening, drying, calcination. The degree of agglomeration can bechosen so that the monolith remains intact until it enters the issue ofthe intestine and subsequently disintegrates into the nanosizeparticles. This naturally results in loss of the transport channels, butthe active compound can still be retained in the mesopores or microporesof the particles and thus be carried in these fragments into thebloodstream. There, the nanosize particles can dissolve and liberate theactive compound (without ever coming into contact with chemical orphysical barriers).

In this context, it is of particular interest that the PEG used in thematerial of the invention is as such already known as a carrier forproteins, namely in that proteins are modified with PEG to increasetheir transportability (“pegnology”). This would, for example, appear tomake it possible to incorporate proteins homogeneously into the materialof the invention as early as in step (I) by using a mixture of PEG andPEG-modified protein in place of pure PEG. The material can then besolidified in the sol-gel process according to the invention and themonolith can be used directly as peroral formulation.

Preference is also given to the use of the material of the invention asbiodegradable or resorbable (i.e. not calcined or hardened in anotherway) material and its use as biologically integrable ceramic material(bioactive, i.e. calcined, also known as bioglass) in medicaltechnology, in particular for strengthening bone, for supportingconnective tissue and for the healing of wounds.

As regards the above-mentioned carbon-containing monoliths formed bymeans of an after-treatment, preference is given, in addition to theapplications mentioned above, to the following applications:—(i) use asresorbent for substances, e.g. in the case of poisoning phenomena in thehuman body, (ii) as hydrogen store, both as storage material as such andas support material for another storage material.

Carbon-containing monoliths which are based on the siliceous material ofthe invention as template and are formed, as mentioned above, in theafter-treatment of the siliceous material of the invention areparticularly useful as hydrogen stores or as supports for hydrogenstores since they have a large surface area due, in particular, to thehierarchical pore structure. In this context, the use of thesecarbon-containing monoliths in conjunction with finely divided hydridesis of particular interest. Here, particular preference is given to thehydrides of the main group metals and transition metals, e.g. magnesiumhydride which is known as reversible hydrogen store. It is alsoconceivable for hydrides of semi-metals and non-metals to be used incombination with the carbon-containing monolithic material, with mixedhydrides, i.e. hydrides of main group and transition metals withsemi-metals, being particularly preferred. Among mixed hydrides for thehydrogen stores, alanates which contain, for example, Li, Al andhydrogen and are typically used in combination with carbon-containingmaterials, for example carbon nanotubes, are of particular interest. Inthe context of the present invention, the alanates are used incombination with the carbon-containing hierherical monolithic materialof the invention having an at least bimodal pore structure. A hydrogenstore in which the hydrogen can be stored reversibly and released againis particularly preferred here.

Finally, it is also conceivable for the materials of the invention (withor without after-treatment) to be deposited as thin films or be used asbuilding blocks in electric/electronic circuits. Here, their use asdielectrics having a high dielectric constant is of particular interest,since a large pore volume leads to correspondingly good electricalinsulation, a property which is particularly important for theminiaturization of circuits in which “jumping over” of electric chargealways presents a problem. Production and use of the materials accordingto the invention will be illustrated below with the aid of examples,without the generality of the claims according to the present inventionbeing restricted thereby.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a scanning electron micrograph of the inventive materialobtained according to Example 3,

FIG. 2 shows the pore size distribution of decomposable inventivemonoliths according to Example 5,

FIG. 3 shows the pore size distribution for micropores for decomposableinventive monoliths containing amphiphiles according to Example 7,

FIG. 4 shows the overall pore size distribution for the material ofExample 7,

FIG. 5 shows the small angle x-ray diffraction pattern of the materialof Example 7,

FIG. 6 shows the amount of a model drug set free by differentembodiments of the inventive material according to example 10,

FIG. 7 shows the change in concentration of a model drug in a modelbodily fluid as a function of time for the inventive decomposablematerial as described in Example 11.

EXAMPLE 1 Production of a Decomposable Monolith Having a Bimodal PoreStructure

In this example, the general synthetic route for producing adecomposable monolith having a bimodal pore structure will be described.Limits within which the proportion of individual constituents can bevaried will be described in subsequent examples.

In the first step, 0.7 g of polyethylene glycol (PEG) having a molecularweight of 35000 is dissolved in 8.0 g of water and 0.81 g of 60%strength nitric acid. 6.5 g of TEOS are added to this mixture whilestirring. The sol is stirred until a clear solution is obtained and issubsequently poured into moulds and gelled at about 40° C. for 5 hoursand then aged at the same temperature for at least 48 hours.

To increase the degree of condensation and to control the size of themesopores, the gel is subjected to solvent replacement at 90° C. in 1 Mammonium hydroxide solution for 9 hours. The volume of the solvent isabout 10 times the volume of the gel. After solvent replacement iscomplete, the monoliths are washed with 0.1 M HNO₃ solution and 25%strength ethanol.

In the drying step, the green bodies are dried at 60° C. for 3 days. Themonolith obtained after this displays all characteristic properties ofthe material according to the invention, for example, a bimodal porestructure, transport channels, absence of Bragg reflections. After thedrying step, the monolith can be calcined at 450° C. for 5 hours, withthe temperature being ramped up at 1 K/min.

EXAMPLE 2 Dependence of the Pore Structure on the Molecular Weight ofPEG

The table at the bottom of this example shows how the pore structure(determined visually from scanning electron micrographs and bymeasurement of the porosity using Hg porosimetry) changes as a functionof the molecular weight (MG) of PEG:

As can be seen from the table, the size of the macropores and the degreeof mutual crosslinking can be adjusted by varying the molecular weightof PEG. Pore type MW of PEG Transparency Pore size (SEM) (SEM)   600transparent none none  4 600 transparent <<1 μm isolated 10 000 opaque  <1 μm isolated 35 000 opaque ca. 20 μm connected channels

EXAMPLE 3 Dependence of the Pore Structure on the Relative PEG Content

The following table shows how the pore structure (determined visuallyfrom scanning electron micragraphs and by Hg porosimetry measurements)changes as a function of the relative PEG content (measured in percentby weight) when the molecular weight of PEG is kept constant at 35000PEG (MG 35000) Weight % by Trans- Pores: SEM Sample [g] weight parencySize Type K1 0.4 2.55 opaque 10-20 μm isolated K2 0.5 3.17 opaque 30-80μm mainly isolated K3 0.6 3.78 opaque 5-10 μm partly connected K4 0.74.38 opaque 20-40 μm partly connected K5 0.8 4.98 opaque 3-7 μm partlyconnected K6 0.9 5.56 opaque 1-2 μm partly connected K7 1.0 6.14 opaque<1 μm separated

As can be readily seen from the table, the size of the macropores andthe degree of connection of the pores to form channels can once again beinfluenced by varying the relative PEG content. The macropores connectedto form channels in the sample K5 are shown in a scanning electronmicragraph having a scale of 1 cm≡30 μm in FIG. 1.

EXAMPLE 4 Dependence of the Pore Structure on the Relative TEOS Contact

The following table shows how the pore structure (determined visuallyfrom scanning electron micragraphs and by Hg porosimetry measurements)changes as a function of the relative TEOS content (measured in percentby weight). r value of Particle size Pore Type TEOS Transparency (SEM)(SEM) 20.57 opaque  5-10 μm particles 17.14 opaque 10-20 μm connectedchannels 14.7 opaque 25-50 μm connected channels 12.86 opaque 10-20 μmisolated 11.43 opaque 30-80 μm isolated

EXAMPLE 5 Dependence of the Pore Structure on the Concentration of theSolvent in the Solvent Replacement

The concentration of the solvent used in the solvent replacement step(here: ammonium hydroxide replaces nitric acid) is of particularimportance in determining the size of the mesopores (measured by meansof absorption measurements using nitrogen). Here, the change insignificant pore parameters (surface area, pore volume, pore diameter)with changes in the concentration of ammonium hydroxide (1.0 M, 0.1 M,and 0.01 M) is shown at various temperatures.

The assignment of the sample to the respective temperature atconcentration of ammonium hydroxide is as shown in the following tableTemperature 22° C. 40° C. 60° C. 90° C. Concentration  1.0 M S1a S2a S3aS4a NH₄OH  0.1 M S1b S2b S3b S4b 0.01 M S1c S2c S3c S4c

and the pore parameters for the samples are shown in the table below:Pore diameter Surface area Pore volume [nm] Sample [m²/g] [cm³/g]Absorption Desorption S1a 449.38 1.271 12.32 10.02 S1b 801.41 1.316 7.596.62 S1c 902.10 0.802 4.22 3.86 S2a 368.68 1.403 17.69 14.13 S2b 623.061.346 10.32 8.88 S2c 835.57 1.227 6.88 6.10 S3a 260.04 0.636 11.49 10.88S3b 497.81 1.353 14.46 11.09 S3c 646.07 1.250 9.44 8.19 S4a 235.46 0.50010.89 10.32 S4b 373.40 1.149 18.48 15.30 S4c 512.88 1.242 11.39 9.68

Pore distribution functions for mesopores and macropores of decomposablemonoliths produced by the general procedure described in Example 1 andsubjected to solvent replacement at 90° C. at various concentrations ofammonium hydroxide are shown in FIG. 2. In this figure, the horizontal xaxis gives the mean pore diameter (in microns) and the vertical y axisgives the measured proportion of pores at this diameter (measured inmillilitres per gram). The continuous line corresponds to a 2 M ammoniumhydroxide solution, the broken line corresponds to a 0.2 M solution andthe dotted line corresponds to a 0.02 M ammonium hydroxide solution. Thegraph thus clearly demonstrates that, in particular, the size of themesopores can be set reproducibly via the concentration of ammoniumhydroxide.

EXAMPLE 6 Production of a Decomposable Monolith Having a Trimodal PoreStructure

To obtain the sol, 0.62 g PEG having a molecular weight of 35000 ismixed with 5.5 g of water and 1.3 g of nitric acid. 5.05 g of TEOS areadded to this mixture and the mixture is stirred until a clear solutionis formed.

At this point, 0.36 g of C₁₄TAB as amphiphile are added to the sol. Thismeans that in this example the PEG content is 4.84% by weight and theC₁₄TAB content is 2.78% by weight. The sol is subsequently poured intomoulds, gelled at 40° C. for 5 hours and then aged at 40° C. for 48hours.

The monolith is then subjected to solvent replacement at 90° C. in 1 Mammonium hydroxide solution for 8 hours. The volume of the solvent isabout 10 times the volume of the gel. After solvent replacement iscomplete, the green body is washed with 0.1 M HNO₃ solution and 25%strength ethanol.

In the drying step, the green bodies are dried at 60° C. for 3 days andsubsequently calcined at 500° C. for 5 hours, with the temperature beingramped up at 1 K/min. For monoliths having a trimodal pore structure,calcination is an important step since the C₁₄TAB can be removedquantitatively in this way.

EXAMPLE 7 Variation of the Size of the Micropores by Choice of theAmphiphile

The production of the monolith is carried out exactly as described inexample 6, except that C16TAB and C18TAB are now used in place ofC14TAB. The influence of the choice of amphiphile on the size of themicropores is shown in FIG. 3. Here, the horizontal x axis gives thepore diameter in nanometers and the vertical y axis gives the porevolume corresponding to the respective pore diameter in cubiccentimetres per gram. The diameter of the micropores can clearly beshifted to smaller values by lengthening the aliphatic chain of theamphiphile.

The overall trimodal pore structure of a decomposable monolith obtainedwith addition of an amphiphile (here C₁₆TAB) is shown by way of examplein FIG. 4, where the horizontal x axis gives the pore diameter inmicrons and the vertical y axis gives the content of the correspondingpores, measured in cubic centimetres per gram. The proportion ofmicropores and mesopores was determined by means of nitrogen adsorption(dotted line) and the proportion of mesopores and micropores wasdetermined by means of Hg porosimetry (continuous line).

In addition, FIG. 5 shows a small angle X-ray diffraction pattern of thetrimodal monolithic material produced using C₁₆TAB The scattering angleto 2Θ in degrees (recorded at the energy of the Cu Kα line) is shown onthe horizontal x axis and the relative scattering intensity in arbitraryunits is given on the vertical y axis. It can clearly be seen that onlythe scattered X-rays decreasing from the primary beam (at 0° C.) typicalof small angle scattering is observed, but not the Bragg reflectionstypical of materials containing mesopores (see discussion in theintroduction). This demonstrates that the material of the presentinvention is in fact disordered on all length scales.

EXAMPLE 8 Materials According to the Invention Having Active MetalCentres by Cohydrolysis of TEOS with a Metal Alkoxide

The materials according to invention describe in the following examplewere produced by the method described in Example 1. The following tablesgives an overview of the amount of starting materials used: PEG [g]Water [g] NH03 35% [g] TEOS [g} Batch 1 1.78 15.82 3.73 14.50 Batch 21.08 16.82 3.73 14.50 Batch 3 0.34 15.82 3.73 14.50

The niobium precursor used is a niobium alkoxide (niobium ethoxide).This was mixed with the TEOS and then added to the polymer solutionacidified with nitric acid.

The following table gives an overview of the experiments carried out andthe properties of the materials after drying and calcination at 400° C.PEG Stability of Comment on the No. [%] PEG/Si H20/Si Nb/Si the monolithstructure of the monolith BET[m²/g] Batch 1 M24/1 4.97 0.58 14.66 0.00stable uniform 161.9 M24/2 4.97 0.58 14.55 0.27 stable uniform 165.1M24/3 4.97 0.58 14.55 0.54 stable uniform 163.3 M24/4 4.97 0.58 14.552.68 stable uniform 152.9 M24/5 4.97 0.58 14.55 5.35 stable uniform, nobubbles 151.2 M24/6 4.97 0.58 14.55 26.76 unstable very soft and crumblyBatch 2 M24/7 3.02 0.35 14.55 0.00 stable uniform 185.1 M24.8 3.02 0.3514.55 0.54 stable uniform 178.2 M24/9 3.02 0.35 14.55 5.35 stableuniform, no bubbles 163.7 M24/10 3.02 0.35 14.55 26.76 unstable verysoft and crumbly 128.7 Batch 3 M24/11 0.99 0.11 14.55 0.00 unstable verysoft and crumbly 116.5 M24/12 0.99 0.11 14.55 0.54 unstable very softand crumbly 114.7 M24/13 0.99 0.11 14.5 5.35 unstable very soft andcrumbly 101.4 M24/14 0.99 0.11 14.55 26.76 unstable very soft andcrumbly 128.2

The materials were examined before uniformity of the niobiumdistribution by means of X-ray fluorescence, giving the followingfindings: (i) the above of niobium introduced into the synthesis gelwere found in the ceramic product and (ii) the niobium introduced isdistributed uniformly over the shaped body.

Shaped bodies produced by the above-described method using tantalumethyoxide, titanium ethyoxide and zirconium ethyoxide in place of theniobium ethyoxide likewise display uniform metal distributions in thesiliceous matrix.

EXAMPLE 9 Materials According to the Invention Having Active MetalCentres by After-Treatment of the Porous Monolith with a Metal SaltSolution

A monolith produced as described in Example 1 (SiO₂) was activated in aSchlenk flask at 90° C. under an oil pump vacuum for a period of 12hours. After 12 hours, the flask was cooled to room temperature andflushed with oxygen- and water-free argon. 10 ml of a 0.01 molarsolution of vanadium (V) isopropoxide in anhydrous ethanol wasintroduced through a septum (=bringing into contact). The monolith washeated in the solution at 50° C. for 3 hours, and the solvent wassubsequently removed via a Schlenk frit and the monolith was evacuatedat 90° C. for 12 hours. This material, too, displays uniform loadingwith metallic centres and can optionally be calcined.

EXAMPLE 10 Use of the Inventive Porous Monolithic Material in the Fieldof Drug Release

Four different materials have been used, namely (i) as sample Q4, thesample from Example 1 with the difference that the molecular weight ofthe PEG is 10.000 (diameter of the mesophores: 14 nm), (ii) a sample P4,the sample K5 from example 3 containing an additional 0.5% by weight ofC₁₆ TAB (11.3 nm of pore diameter), (iii) as sample P6, sample K5containing 3.0% by weight of C₁₆ TAB (7.6 nm of pore diameter) andfinally (iv) as sample R2, sample K5 from example 3 in which a solventexchange has been performed in 0.21 m Ammoniumhydroxyde (11 nm of porediameter).

These samples have been loaded with ibuprofen (diameter of the samples:approximately 0.6 nm) by means of soaking of the monoliths in hexanecontaining ibuprofen as a desolved drug for three days. Afterwards, themonoliths have been cleaned carefully with hexane and have been driedfor one day. The amount of ibuprofene taken up was determined by meansof UV-VIS spectroscopy and by means of conventional weighing (seeTable). UV-VIS Change of weight Adsorbed Adsorbed Mass Mass SampleWeight [mg] [mg] Weight % [mg] Weights % Q4 648.3 107.6 16.6 124.4 19.2P4 299.5 49.4 16.5 61.2 20.4 P6 312.8 73.5 23.5 84.2 26.9 R2 331.4 73.922.3 83.2 25.1

In the above Table, the adsorbed mass in column 3 has been determined bymeans of UV-VIS spectroscopy while the absorbed mass in column 5 hasbeen determined by measuring the change in weight. In order toinvestigate the effectiveness of the drug release, the samples have beensoaked into a liquid that corresponds to human bodily fluids (at 40° C.)and the concentration of ibuprofen within the liquid has been measuredby means of UV-VIS spectroscopy. The amount of ibuprofen set free in theliquid shown in FIG. 6. Here the horizontal axis shows the time in hoursand the vertical axis shows the amount of ibuprofen that has beenreleased, given in % with respect to the amount of ibuprofen that hadbeen incorporated into the monoliths at the beginning of the experiment.

As can be seen from FIG. 6, the time at which the drug is released canbe determined and/or influenced by the size of the mesophores (as wellas by the type of excanging the solvent). As has been expected, the drugrelease is inhibited for longer times the smaller the pores are.

EXAMPLE 11 Loading and Drug Release in the Inventive Monolithic Materialthat has Not Been Calcined

A decomposable monolith as described in example 6 has been charged witha material, in this case methylene blue, after the drying step at 80° C.(i.e. without a step of calcining) by means of equilibrium absorption.The achieve this, the material has been dipped into a 0.01 m solution ofmethylene blue in ethanol. The methylene blue is used to model apharmaceutical drug. After a given period, the monolith has been removedfrom the solution and cut in half. By means of optical analysis thedistribution of the dye over the cross sectional area of the shaped body(monolith) has been measured. This optical analysis shows that afterapproximately 240 min, an even distribution of the dye over the entiremonolith can be found. It is therefore shown that the inventive materialcan be charged even without having been calcined. The effect of chargingis clearly discernable even after having soaked the monolith for about10 minutens. A gradient between the inner and the outer surface isclearly discernable in this case.

To monitor the “drug” release a monolithic material as described abovehas been soaked for 24 hours in a dye solution and was then dried andadded to a 0.1 m solution of HCl (in order to simulate a physiologicalsolution). FIG. 7 shows the change in dye concentration as measured inthe originally pure 0.1 mHCl solution after adding the monolith that hasbeen charged with methylene blue. The Figure shows the dye concentrationgiven in mol/l on the vertical axis as a function of time given inminutes on the horizontal axis.

In summary, it can be stated that this examples shows that (a) theinventive materials can be loaded or charged with a substance even incase the step of calcining is omitted and it can be shown that (b) arelease of the model substance (dye) is possible after the chargingprocess under physiological conditions.

1. Monolithic ceramic material having micropores and mesopores ormesopores and micropores or micropores, mesopores and micropores,characterized in that it is at least partially decomposable underphysiological conditions.
 2. Material according to claim 1,characterized in that structural examination by means of X-raydiffraction displays no Bragg reflections in the small angle region. 3.Material according to claim 1 or 2, characterized in that at least partof the macropores and mesopores or macropores or mesopores present inthe material form transport channels running through at least of thematerial.
 4. Material according to at least one of the preceding claims,characterized in that the pore size has at least one property from thefollowing group: the size of the macropores is from 0.1 μm to 100 μm,the size of the mesopores is from 5 nm to 50 nm and the size of themicropores is from 1 nm to 3 nm.
 5. Material according to at least oneof the preceding claims, characterized in that, after drying, itcontains a higher proportion, measured in percent by weight, ofinorganic constituents then of organic constituents.
 6. Materialaccording to at least one of the preceeding claims, characterized inthat it has at least one active metal center integrated into the porestructure.
 7. Process for producing a monolithic ceramic material whichhas micropores and mesopores or mesopores and macropores or micropores,mesopores and micropores and is at least partially decomposable underphysiological conditions, characterized in that the process comprises atleast the following steps: (I) bringing a precursor material, awater-soluble polymer, an amphiphilic substance and a hydrolysiscatalyst into contact with one another; (II) inducing the sol-geltransition of the mixture from (I); (III) at least partially removingand replacing the solvent in the gel from (II) or at least partiallyremoving or replacing the solvent: (IV) drying the green body obtainedfrom (III).
 8. Process according to claim 7, characterized in that anadditional calcination step (V) (V) calcining the dried green body, iscarried out after step (IV).
 9. Process according to claims 7 or 8,characterized in that the precursor material used in (I) contains atleast one component containing a metal.
 10. Process for producing amonolithic ceramic material which has mesopores and macropores and is atleast partially decomposable under physiological conditions,characterized in that the process comprises at least the followingsteps: (I) bringing a precursor material, a water-soluble polymer and ahydrolysis catalyst into contact with one another; (II) inducing thesol-gel transition of the mixture from (I); (III) at least partiallyremoving and replacing the solvent in the gel from (II) or at leastpartially removing or replacing the solvent: (IV) drying the green bodyobtained from (III); (V) calcining the dried green body at temperatureswhich do not exceed 500° C. at any point,
 11. Process according to claim10, characterized in that the precursor material used in (I) contains atleast one component containing a metal.
 12. Process according to atleast one of claims 7 to 11, characterized in that the precursormaterial is selected from the group consisting of completelyhydrolysable alkoxides, alkoxides having at least one group which cannotbe hydrolysed; halides which are decomposable in aqueous solution,polymerizable metal salts, oligomeric precursor materials, organicallymodified silicates; coordination compounds having carboxyl or β-dicetonligands; and combinations of two or more of the abovementionedsubstances.
 13. Process according to at least one of claims 9 or 11,characterized in that the metal-containing component(s) of the precursormaterial is/are selected from the group consisting of organometalliccompounds, metallocenes, metallic colloid, metal alkoxides andcombinations of two or more of the abovementioned substances. 14.Process according to at least one of claims 7 to 13, characterized inthat the hydrolysis catalyst is selected from the group consisting ofbasic substances such as ammonium, amines, ammonium ions solutions;acidic substances such as mineral acids, organic acids,fluoride-containing solutions; and combinations of two or more of theabovementioned substances.
 15. Process according to at least one ofclaims 1 to 14, characterized in that the water-soluble polymer isselected from the group consisting of uncharged and ionic polymers, andcombinations and mixtures of two or more of the abovementionedsubstances.
 16. Process according to at least one of claims 1 to 15,characterized in that TEOS or a metal alkoxide or TEOS and a metalalkoxide is used as precursor material, nitric acid is used ashydrolysis catalyst, PEG is used as water-soluble polymer and CTAB isused as optional amphiphilic substance, and in that the PEG content isin the range from 2 to 10% by weight, based on the total weight, in thatthe molecular weight of the PEG is from 10000 to 50000, in that therelative proportion of TEOS, given as the “r” value, is in the rangefrom 10 to 20, in that the proportion of CTAB which is used optionallyis from 0.01 to 5% by weight, based on the total weight, and in that thesolvent for the solvent replacement is ammonium hydroxide.
 17. Processaccording to at least one of claims 1 to 16, characterized in that thematerial of the invention is subjected to an after-treatment which maybe selected from the group consisting of: impregnating the monolithicceramic material with, or bringing it into contact with, catalyticallyactive substances, organic compounds or mixtures or further auxiliariesor additives, functionalising at least parts of the internal surface,lipophilising the material; successively loading the pores and allcombinations of two or of the above steps.
 18. Process according toclaim 17, characterized in that the substance or substances for theimpregnation or contacting comprises at least one carbon-containingprecursor compound which contains at least one carbon atom.
 19. Processaccording to claim 17 or 18, characterized in that the carbon-containingmaterial of the invention is calcined at temperatures above 500° C.under nitrogen after impregnation or contacting and is subsequentlycarbonized under reduced pressure.
 20. Process according to at least oneof claims 17 to 19, characterized in that the material of the inventionin calcined after the after-treatment.
 21. Material obtainable by aprocess according to any of claims 7 to
 20. 22. Use of the monolithicceramic material according to at least one of claims 1 to 6 or themonolithic ceramic material obtainable by a process according to atleast one of claims 7 to 20 as all-active catalyst, as catalyst support,as molecular sieve, as biological separator, having a sharp cut offcriteria in respect of the molecular weight, as osmotic membrane or asdielectric medium.
 23. Use of the monolithic ceramic material accordingto at least one of claims 1 to 6 or the monolithic ceramic materialobtainable by a process according to at least one of claims 7 to 20 forthe temporally delayed and temporally controlled and regionally definedsupply of substances of dyes, cosmetic active compounds, auxiliaries oradditives, pharmaceutical relative substances, proteins, peptides,enzymes, active compounds derived from plants, nutrients or nutrientadditives, animal feeds or animal feed additives, fragrance or flavours.24. Use of the monolithic ceramic material according to at least one ofclaims 1 to 6 or the monolithic ceramic material obtainable by a processaccording to at least one of claims 7 to 20 as biodegradable orbiologically resorbable or as biologically integrable ceramic materialin medical technology, in particular for strengthening bone, forsupporting connective tissue and for the healing of wounds.
 25. Use ofthe monolithic carbon-containing material obtainable by a processaccording to at least one of claims 17 to 20 as storage material forhydrogen or as support material for a hydrogen storage material.
 26. Useof the monolithic carbon-containing material obtainable by a processaccording to at least one of the claims 17 to 20 in combination with ordoped with at least one medium capable of reversibly storing hydrogenselected from the group consisting of hydrides of the main group andtransition metals, semimetal hydrides, mixed hydrides, alanates andmixtures of at least two of this substances.